This invention relates to dielectric ceramic compositions and to capacitors having a single or multiple layered ceramic body of such compositions.
A variety of dielectric ceramic compositions have been suggested and used for capacitors with a view to greater capacitance. Among such known compositions are those composed primarily of barium titanate (BaTiO.sub.3), or of a compound obtained by partly substituting calcium (Ca) for barium (Ba), and zirconium (Zr) for titanium (Ti), of BaTiO.sub.3. It has also been known to add manganese compounds to such compositions. Ceramic capacitors of these known compositions possess specific dielectric constants of up to 14,000 or so.
There are, however, strong, consistent demands from electric and allied industries for dielectric ceramic capacitors of even greater capacitance and other performance characteristics. One obvious solution to the problem of how to increase the capacitance of monolithic ceramic capacitors is to reduce the thickness of the ceramic body between the pair of electrodes. This solution works only to a limited extent, however, because too much reduction in the thickness of the ceramic body would make the voltage withstanding capabilities of the capacitors inconveniently low. The only practical solution is therefore to use dielectric ceramics of higher specific dielectric constants and higher voltage withstanding capabilities than those attainable with conventional materials including those composed principally of BaTiO.sub.3 or the like.
Another inconvenience heretofore encountered in the manufacture of ceramic capacitors is that some ceramic materials have to be sintered at temperatures as high as 1300.degree. C. or more. Such high sintering temperatures have required the use of palladium as a material of electrodes in cosintering these electrodes with the ceramic bodies. Palladium is currently very expensive and has added substantially to the costs of ceramic capacitors. The advent of ceramic materials that are sinterable at lower temperatures has been awaited to enable use of less expensive electrode materials.